Swath Boat building Plans

Discussion in 'Boat Design' started by blackdaisies, Sep 1, 2008.

  1. Munter
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    Munter Amateur

    BMcF has it right. A swath craft won't develop righting moment because the center of displacement doesn't move to leeward to the same extent as a regular cat. Think about it some more.

    The ability to remain stable in waves doesn't equal the ability to resist heeling moment from a rig.
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Blackdaises
    I have designed 3 SWATHs all in service and several more on paper, which never got to production. SWATHs have a very limited range of usage. If your no.1 goal is seakeeping and nowt else, then go for a SWATH. Otherwise a catamaran will suffice.

    If you are really keen on SWATHs, then first you need to do a basic layout and ascertain what you reckon the displacment will be. From that, you'll know whether you can design/build a SWATH to meet that criterion. It is not as straight fwd as designing a simple multihull. Since im sure you'll find that there wont be enough buoyancy (too heavy) or you'll want more power/speed, which will lead to bigger engines and hence larger submerged tubes etc etc...and on it goes.
     
  3. BMcF
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    BMcF Senior Member

    Yeah..what do I know? I've only been involved in building and providing/installing/sea-trialing the stabiization package for 11 SWATH over the last 20 years, ranging in size from a baby of only 35' (camera platform for '87 Americas Cup races) to the largest at 38 meters LOA. And lots more designs that have not seen water..

    You would quickly be educated without further discussion if I could simply invited you to board one of the USN 40' minehunting SWATHS we did with SOS..its kinda funnny when only one person at a time can board a 40' vessel and must proceed to the opposite deck edge to allow the next to board. That will teach you all you don't yet understand about SWATH 'stability'..or almost total lack thereof.:D The 35' was even more tender..yet all of them were amazing sea-keeping machines once they were at speed and the automatic fin stabilization system got a good bite...

    We were involved in one 'very fast' SWATH..a 90' vessel that was built as a yacht. The same installed power in a similarly-sized catamaran would have made a top spped of 35 knots or more..the SWATH managed about 23...which is fast for a SWATH. Very fast. Their high resistance is the price to be paid for their seakeeping capabilites.
     
  4. yipster
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    yipster designer

    you know it but thanks for telling nevertheless BCmF, i got a hard chine and round ama file ready for michlett to compare that again opens with a swath, interesting stuff :)
     
  5. Qhiron
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    Qhiron Junior Member

    Swath instability

    Thx, BF I understand your points, and appreciate the sharing. And after min. thought, you are so right. Duh. my last reply was on an iphone, tiny letters hard to read.

    As you stated at speed, few probs with stability and control. This can be refined by gyros, computer program and adjust. fins, re: heeling. (affecting drag too). Munter, at ANY speed that kind of 'adjustment' is correctable, right?

    I agree that anything over the water, planing, is much more efficient then plowing through it, below. OK. My contention of swath design is that plowing- stability under way and wave motion resistance. For lux yacht platforms, this would seem to be high on priorities list, not whether this BOAT is fastest. With the sophistication of a technologies adjusting platform attitude and stability derivatives/trim: list, heel and toe amplitude should be correctable.

    Also structurally, back to my original Q's,
    it would seem to be operating under different stress criteria with swath- factors because of this = lighter weight above, better effective habitable volume. I am just trying to find an ideal dimension for the platform.
    With adjustable 'wings' with the submerged pontoon hulls, at varying angles to the platform itself, wouldn't the trim considerations become secondary, at any speed?
    And this michlett calc thing you pros quote is intriguing
    There is actually an easy way of calcing dynamic curved volumes and defining shaps? What you using, Katia?

    This is what I mean, by balancing sail rig with vessel, and vessel with configuration of pontoons. Long underwater buoyant bodies....
    Gives me a new idea: Quad, independent torpedo hulls, each connected like an adjustable spider/arm/wing to central platform. minor amplitude operable gimbals adjusts each torpedo individually according to stated forces and direction of motion under water.
    Wouldn't this
    resolve your heel tendency? (yes, at increased drag)
    Think of those little waterskimmer bugs, sitting above the surface, but now with each leg having a submerged propulsion torpedo foot.

    maybe a new thread on this.

    Wow, imagine the properties of a quad-motorized, highly efficient propelled water jets, within each torpedo. Connected to hydro-dynamic, long, gullwing shaped winglets. Main hull has the diesel with generator, power feed to indiv. electric motors, submerged.
    Who of you (BMcF) was working for DoD? Wouldn't they love to see this?
    Four adjustable pod legs, with hyperspeed-type torpedo technology, always submerged. Arms can adjust platform height above surface, drop down to low observable profile, or scoot up high on plane to range, increase horizon exposure.
    Turns on a dime, totally stable (under motion_) exo-skeleton construction
    incredible speed capability, and dynamically adjustable surface profile....

    scale:
    -one man pod, prone forward position, 25' x 40' attack and recon,
    or a full destroyer class multihull. 200ft+ Yeowsa!
    hmmm, maybe this idea should be classified...
    yipster: what's ama?
     
  6. masalai
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    masalai masalai

    Qhiron, you talk of adding gyro's for stability - it is a boat man do not make it more complex - just being a boat is enough complexity... ama is like a smaller outer hull in a trimaran, - - or, - in some languages a respected mother of your wife....

    Many of your "bright ideas" are planing type craft so when the sea gets up so does your stomach and the speed goes to dead slow..... i.e. - - won't work nicely - - -

    Think of the meaning of "elegant" and apply that to every aspect of your design fancy - it does not mean "dressed up like a painted harlot" but more minimalist approach of refined beauty and effective efficiency
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    Qhiron
    You need to do a basic design of what you are proposing. Then you'll see it is way over weight and you'll have to change the design and then find it is getting too large and too heavy and too much power required etc etc.
    Saying what you would like or "think" is possible will all fall away when you actually sit down and do a basic design.
    SWATHS are very very weight sensitive. Think of them as a 100m athlete. Excess weight is a killer...gets to the point of no point having a SWATH, unless you're really prepared to pay the penalty, in terms of cost, size, power, displacement etc etc....just see how many SWATHs worldwide there are...very few, why...because one must compromise everything for the seakeeping. It is the panacea of seakeeping, but at an extreme cost. Not everyone is prepared to sacrifice what "they want" for "what they can have" in a SWATH.
    Othwerwise, just keep dreaming....
     
  8. BMcF
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    BMcF Senior Member

    Keen observations Ad Hoc..on the mark. And also illustrative of why there are so many variations in catamaran designs these days that are 'swath-like' or 'semi-swaths' but deviate significantly from the fundamental Creed SWATH characteristics for the reasons of weight sensitivity or powering requirements..or often both. There have also been more than few SWATH 'abortions'; failed or marginal vessel designs that have deviated from Creed's principles, realized first in practice with the 'Kaimalino' simply because they could not or would not deal with the need for , and huge benefits gained from, active fin stabilization. Such incredibly tender vessels required tiny active appendages to perform superbly. Lacking those..well I won't point to what happens by vessel name, but they are out there and they are sorry by comparison.
     
  9. Qhiron
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    Qhiron Junior Member

    Gyros meant only for directional input of data. Masalai. Not mass-inertia directional control.
    Ad hoc I agree weight is critical, but in what application? Certainly subsurface, stronger (heavier ballast) steel/or alum is ok, topside lighter, stressed skin composites better. Remember the trimaran YPE?
    remember low aspect rigid foil sail, skimming pontoon arms that compensated leverage. Macquarie innovations. MI needs perfect weather, I believe.

    Now all records are windsurfers, weight/drag to wind ratios that cannot be beaten by larger vessels. Remember CrossbowII assymetric? Tom something, builder?

    I have a design in mind, drawn, not computerized, many pages.Parameters are important here. Not overall speed, but comfort under sail. Stability. Size determined by scale of applications. When do these moment arms and (cross-vectors of) stress forces simply become too large to deal with using current build terchnology?

    Fascinated by swath sail cats for three reasons: Stability, large cat deck habitable area, dynamic adjustment of draft, height a.w.l., and ease of operation.
    Yes, surface hulls are simpler, but with many different design criteria compromises. Instead of banging into waves, slicing seems better for comfort.
     
  10. masalai
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    masalai masalai

    Then think of complexity of structural integrity and additional strength demanded in that design - There is an Oberon class submarine for sale in Australia for about AU$500,000.oo if that is your bent otherwise what you are postulating is a childhood dream, as to bring it off would require MILLIONS and all for what? Methinks not for socialising....
     
  11. Qhiron
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    Qhiron Junior Member

    Under power swaths, different criteria:
    "Quest", by M.A.P. was insanely unstable.
    "Seashadow" dimensionally better, but again, diff criteria. MW cross sections.
    Take the "Navatech II" remove entire upper hull and replace it with an assymetrical, oblong elyptoid, which cantilevers y/3 (beam) over each side. NOT bow/stern! Cut torps in half, extend arms directionally from cG outward.
    What happens inside, design-wise is easy, except for D.l. weight distribution.

    The single operator "SEASKIMMER" I'm envisioning is much more dynamic. Small diesel/gen engine topside,prone pilot straddles it, center cG gives hi-perf elect. propulsion in torps. DC current. THink of four waverunner jets -ALWAYS submerged- as propulsion. Probably trapezoidal layout for clean water intake, or triplets in triangle planview
     
  12. masalai
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    masalai masalai

    Graphics please
     
  13. BMcF
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    BMcF Senior Member

    Quest illustrates the beauty of what you can do with actively stabilized vessels that have literally zero static stability otherwise. The sky is the limit and mother nature defeated..until a bit bucket overflows or the ones and zeroes get tangled up.
    :D

    Kudos to Danny and Mark for making the Quest fly like she did..and John for pursuing the vision.
     
  14. Qhiron
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    Qhiron Junior Member

    Graphics? You're kidding, M, that's what I get paid for.... LOL!
    Now I have four different design configs I'd like to pursue further.
    TurboCAD just doesn't do too well with compound curves and bitmapped surfaces. And AutoCAD with a MAC G5, noooo way,
    so my cool sketches, which as BF will point out, are anything but realistic-
    but proprietary this is- when I put those lines to paper, I'm under contract. Like Skunkworks, the best stuff is on napkins...
    So who's with Norfolk's GE fastboat Div? (maybe they want a bail out too)
    hence:
    1.) the applications, recreational, milspec or R & D performance?
    2.) industry resources, connections to build
    3.) yep, most important: the client

    BF, you knew this Quest project, you salty dog, you! Must have been really fun!!!! I'm too young for that crowd
    Got two small local outfits who can lasercut any shapes, scaled sizes, but no tub, no facilities to run them in. Northsail is right around the corner from me in MDR. Three navArchs doing dingy designs for Zodiacs, you get the idea.

    May be heading to the Bahamas to start up a deep water rec. harbor, but too many if's...
    "irukandji" would be a good name.


    will see, the will, -the way.
     

  15. BMcF
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    BMcF Senior Member

    LOL..I go further back than that one...;)
     
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